Human systems have to be flexible, but whenever the pendulum goes too far one way, the system can be abused.
Suppose you have been harassed at work and make a complaint to HR. A common policy is to believe the complainant.
Can you see the bug?
If a wrongdoer complains about someone, that can cause a lot of trouble. The wrongdoer will be presumed to be telling the truth despite that the claim is baseless. So much for the presumption of innocence.
Recently, there have been many allegations of abuse within Hollywood and other areas. I expect that many of these allegations are quite truthful. I am concerned that some are not, and my reasoning is given above.